Online Letters to the Editor
The Relationship Between RBC Distribution Width at Hospital Discharge and Out-ofHospital Mortality in Critically Ill Patients To the Editor:
I
n a recent issue of Critical Care Medicine, we read the article by Purtle et al (1). They aimed to evaluate whether red cell distribution width (RDW) had a relationship with increased postdischarge mortality in critically ill patients. They concluded that elevated RDW level at hospital discharge may identify ICU survivors who are at risk for adverse outcomes following hospital discharge. Since this variable has been inexpensive, its use in daily practice may become widespread in the near future. We would like to thank Purtle et al (1) for their comprehensive contribution. RDW, representing an index of heterogeneity of RBCs, is used in the differential diagnosis of anemia in clinical practice (2). Previously, RDW was demonstrated to be an independent variable of prognosis in patients with cardiopulmonary diseases, such as heart failure, myocardial infarction, strokes, pulmonary artery hypertension, and pulmonary embolism (2–6). In addition, several studies have reported that RDW has a significant relationship with cardiac and noncardiac mortality in critically ill patients (7, 8). Aging, malnutrition, erythropoietin use, iron or vitamin B12 deficiency, bone marrow depression, acute or chronic inflammation, infections, antibiotic use, and any medication may affect RDW levels (2, 8). Thus, it would have been better if the authors had mentioned these RDW affecting factors in greater detail. Furthermore, it would have been accurate if the authors had specified the elapsed time between taking the blood samples and measuring RDW, because waiting period prior to analysis may alter RDW levels (2). Finally, the findings of Purtle et al (1) will lead to further researches regarding the relationship between RDW and mortality in critically ill patients. The authors have disclosed that they do not have any potential conflicts of interest. Ergenekon Karagöz, MD, Department of Infectious Diseases and Clinical Microbiology, GATA Haydarpasa Training Hospital, Istanbul, Turkey; Alpaslan Tanoglu, MD, Departments of Internal Medicine and Gastroenterology, GATA Haydarpasa Training Hospital, Istanbul, Turkey
REFERENCES
1. Purtle SW, Moromizato T, McKane CK, et al: The Association of Red Cell Distribution Width at Hospital Discharge and Out-of-Hospital Mortality Following Critical Illness. Crit Care Med 2014; 42:918–929
Copyright © 2014 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins
Critical Care Medicine
2. Karagöz E, Tanoglu A: Red Blood cell distribution width: An emerging diagnostic factor of acute appendicitis? World J Emerg Surg 2013; 8:54 3. Allen LA, Felker GM, Mehra MR, et al: Validation and potential mechanisms of red cell distribution width as a prognostic marker in heart failure. J Card Fail 2010; 16:230–238 4. Dabbah S, Hammerman H, Markiewicz W, et al: Relation between red cell distribution width and clinical outcomes after acute myocardial infarction. Am J Cardiol 2010; 105:312–317 5. Ani C, Ovbiagele B: Elevated red blood cell distribution width predicts mortality in persons with known stroke. J Neurol Sci 2009; 277:103–108 6. Hampole CV, Mehrotra AK, Thenappan T, et al: Usefulness of red cell distribution width as a prognostic marker in pulmonary hypertension. Am J Cardiol 2009; 104:868–872 7. Meynaar IA, Knook AH, Coolen S, et al: Red cell distribution width as predictor for mortality in critically ill patients. Neth J Med 2013; 71:488–493 8. Kim CH, Park JT, Kim EJ, et al: An increase in red blood cell distribution width from baseline predicts mortality in patients with severe sepsis or septic shock. Crit Care 2013; 17:R282 DOI: 10.1097/CCM.0000000000000303
The authors reply:
W
e thank Karagöz and Tanoglu (1) for their response to our study. The respondents highlight some of the important patient characteristics that may influence the magnitude of the red cell distribution width (RDW). Specifically, the authors are interested in aging, malnutrition, erythropoietin use, iron or vitamin B12 deficiency, bone marrow depression, acute or chronic inflammation, infections, and antibiotic or medication use as modulators of RDW. In our study, we analyzed the association of RDW at hospital discharge and subsequent mortality in a large cohort of patients who received critical care and survived hospitalization. We adjusted for covariates that are thought to be potential confounders of the RDW-mortality relationship, including age, race, gender, Deyo-Charlson Index, patient type (medical vs surgical), sepsis, and number of organs with acute failure. In our model, when we additionally adjusted for creatinine, mechanical ventilation, vasopressor/inotrope use, receipt of blood transfusion, and anemia, the RDW-mortality relationship was preserved (2). It is likely that further adjustment of erythropoietin use, iron or vitamin B12 deficiency, and bone marrow depression will have similar model performance as those adjusted for receipt of blood transfusion and anemia as these covariates are highly correlated. Further, RDW has been shown to have a strong, graded association with C-reactive protein and erythrocyte sedimentation rate independent of confounding factors (3). Although we did not add covariates for vitamin B12 deficiency, folate deficiency, iron deficiency, or C-reactive protein (since these are not routinely measured at a standard time point such as hospital discharge), Patel et al (4), studying more www.ccmjournal.org
e485
The Relationship Between RBC Distribution Width at Hospital Discharge and Out-ofHospital Mortality in Critically Ill Patients To the Editor:
I
n a recent issue of Critical Care Medicine, we read the article by Purtle et al (1). They aimed to evaluate whether red cell distribution width (RDW) had a relationship with increased postdischarge mortality in critically ill patients. They concluded that elevated RDW level at hospital discharge may identify ICU survivors who are at risk for adverse outcomes following hospital discharge. Since this variable has been inexpensive, its use in daily practice may become widespread in the near future. We would like to thank Purtle et al (1) for their comprehensive contribution. RDW, representing an index of heterogeneity of RBCs, is used in the differential diagnosis of anemia in clinical practice (2). Previously, RDW was demonstrated to be an independent variable of prognosis in patients with cardiopulmonary diseases, such as heart failure, myocardial infarction, strokes, pulmonary artery hypertension, and pulmonary embolism (2–6). In addition, several studies have reported that RDW has a significant relationship with cardiac and noncardiac mortality in critically ill patients (7, 8). Aging, malnutrition, erythropoietin use, iron or vitamin B12 deficiency, bone marrow depression, acute or chronic inflammation, infections, antibiotic use, and any medication may affect RDW levels (2, 8). Thus, it would have been better if the authors had mentioned these RDW affecting factors in greater detail. Furthermore, it would have been accurate if the authors had specified the elapsed time between taking the blood samples and measuring RDW, because waiting period prior to analysis may alter RDW levels (2). Finally, the findings of Purtle et al (1) will lead to further researches regarding the relationship between RDW and mortality in critically ill patients. The authors have disclosed that they do not have any potential conflicts of interest. Ergenekon Karagöz, MD, Department of Infectious Diseases and Clinical Microbiology, GATA Haydarpasa Training Hospital, Istanbul, Turkey; Alpaslan Tanoglu, MD, Departments of Internal Medicine and Gastroenterology, GATA Haydarpasa Training Hospital, Istanbul, Turkey
REFERENCES
1. Purtle SW, Moromizato T, McKane CK, et al: The Association of Red Cell Distribution Width at Hospital Discharge and Out-of-Hospital Mortality Following Critical Illness. Crit Care Med 2014; 42:918–929
Copyright © 2014 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins
Critical Care Medicine
2. Karagöz E, Tanoglu A: Red Blood cell distribution width: An emerging diagnostic factor of acute appendicitis? World J Emerg Surg 2013; 8:54 3. Allen LA, Felker GM, Mehra MR, et al: Validation and potential mechanisms of red cell distribution width as a prognostic marker in heart failure. J Card Fail 2010; 16:230–238 4. Dabbah S, Hammerman H, Markiewicz W, et al: Relation between red cell distribution width and clinical outcomes after acute myocardial infarction. Am J Cardiol 2010; 105:312–317 5. Ani C, Ovbiagele B: Elevated red blood cell distribution width predicts mortality in persons with known stroke. J Neurol Sci 2009; 277:103–108 6. Hampole CV, Mehrotra AK, Thenappan T, et al: Usefulness of red cell distribution width as a prognostic marker in pulmonary hypertension. Am J Cardiol 2009; 104:868–872 7. Meynaar IA, Knook AH, Coolen S, et al: Red cell distribution width as predictor for mortality in critically ill patients. Neth J Med 2013; 71:488–493 8. Kim CH, Park JT, Kim EJ, et al: An increase in red blood cell distribution width from baseline predicts mortality in patients with severe sepsis or septic shock. Crit Care 2013; 17:R282 DOI: 10.1097/CCM.0000000000000303
The authors reply:
W
e thank Karagöz and Tanoglu (1) for their response to our study. The respondents highlight some of the important patient characteristics that may influence the magnitude of the red cell distribution width (RDW). Specifically, the authors are interested in aging, malnutrition, erythropoietin use, iron or vitamin B12 deficiency, bone marrow depression, acute or chronic inflammation, infections, and antibiotic or medication use as modulators of RDW. In our study, we analyzed the association of RDW at hospital discharge and subsequent mortality in a large cohort of patients who received critical care and survived hospitalization. We adjusted for covariates that are thought to be potential confounders of the RDW-mortality relationship, including age, race, gender, Deyo-Charlson Index, patient type (medical vs surgical), sepsis, and number of organs with acute failure. In our model, when we additionally adjusted for creatinine, mechanical ventilation, vasopressor/inotrope use, receipt of blood transfusion, and anemia, the RDW-mortality relationship was preserved (2). It is likely that further adjustment of erythropoietin use, iron or vitamin B12 deficiency, and bone marrow depression will have similar model performance as those adjusted for receipt of blood transfusion and anemia as these covariates are highly correlated. Further, RDW has been shown to have a strong, graded association with C-reactive protein and erythrocyte sedimentation rate independent of confounding factors (3). Although we did not add covariates for vitamin B12 deficiency, folate deficiency, iron deficiency, or C-reactive protein (since these are not routinely measured at a standard time point such as hospital discharge), Patel et al (4), studying more www.ccmjournal.org
e485
